The invention relates to a sensor plate for electronic measurement of an applied load, such as, the weight of an object. The load is applied to the sensor plate, causing the sensor plate to undergo resilient strain in proportion to the applied load. One or more electronic sensors are permanently affixed on the sensor plate to sense the strain. Each of the sensors produces an electrical signal that varies in proportion to the strain. The signal can be electronically calibrated to indicate the amount of the load. For example, the sensor plate is deployed in a platform scale to sense the weight of an object, and produce a calibrated reading of the weight. Further, for example, the sensor plate is deployed in a microwave oven to weigh a quantity of food, and to produce calibrated adjustments of power level and duration of a microwave energy output to defrost and/or cook the food. A platform scale and a microwave oven are but examples of many different devices that deploy a sensor plate. What is needed is a sensor plate that would be adapted for use in many different devices. Further, a desirable sensor plate would be of compact construction having a minimum parts count.
U.S. Pat. No. 6,417,466 discloses a sensor plate that is machined to shape the sensor plate with narrow flexure beams. When a load is applied to the sensor plate, the strain becomes concentrated in each narrow flexure beam. A sensor plate made by machining is more costly than a sensor plate made by a stamping and forming operation, also referred to as coining.
Each of U.S. Pat. Nos. 4,548,086 and 4,993,506 discloses a sensor plate that is made from one flat piece, which is suitable for stamping and forming, also referred to as coining. One disadvantage of a flat piece sensor plate is that it does not self-limit the strain imposed by an excessive applied force. Accordingly, the flat piece will undergo inelastic deformation in response to an excessive applied force, and will become permanently deformed. It would be advantageous for a sensor plate that is ideally suitable for stamping and forming, also referred to as coining, and which self-limits the strain in response to an excessive applied force.
According to U.S. Pat. No. 4,993,506 one portion of the sensor plate is required to be attached by screws to a weighing scale apparatus, and another portion of the sensor plate is installed on a weighing platform with raised pads that adhesively secure to the weighing platform and further, that are snap fit onto the sensor plate. This sensor plate requires direct connections to different parts of a weighing scale apparatus. It would be advantageous for a sensor plate that is adapted for drop-in assembly, instead of direct connections to different parts of an apparatus in which it is installed.
Further, according to U.S. Pat. No. 4,993,506, the sensor plate has U-shaped members. This construction requires that an applied load must be summed among smaller forces that are divided among the tips of the U-shaped members to deflect the same. The sensor plate would inaccurately sense the sum of the forces when the forces are directed off-axis to the direction of deflection of the tips. It would be desirable for a sensor plate to not require multiple locations on the sensor plate for receiving an applied load.
U.S. Pat. No. 4,548,086 discloses a push rod that impinges against the sensor plate. The push rod positions the applied load to a precise location on the sensor plate. The push rod is supported in its own housing piece. Accordingly, the push rod and its housing piece increase the parts count and require a construction of increased height, due to the length of the push rod. It would be advantageous for a sensor plate that would not need a push rod.